Method and apparatus for communication link adaptation for interference-canceling receivers

ABSTRACT

Network-side and device-side methods and apparatuses improve transmit link adaptation for devices operating in a cellular network that have interference-canceling receivers. Own-cell link adaptation towards a device in a current transmission interval exploits a determined mapping between the interfering-signal cancelation efficiency of the device versus the interfering-signal transport format, in combination with actual knowledge of the transport format that will be used to make an interfering neighbor-cell transmission in the current transmission interval. For example, a serving radio node uses the known transport format of the interfering transmission, to accurately determine the expected cancellation efficiency for the device with respect to the interfering transmission, and uses the expected cancellation efficiency to obtain a more accurate estimate of the own-cell channel quality expected for the device in the current transmission interval. Link adaptation towards the device in the current transmission interval uses this more accurate estimate of own-cell channel quality.

RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.61/898,047, filed on 31 Oct. 2013, the content of said applicationincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention generally relates to cellular communicationnetworks and particularly relates to link adaptation in such networkstowards receivers with interference-canceling receivers.

BACKGROUND

In order to meet higher capacity demands and enhanced user experiences,cellular communications networks such as Long Term Evolution, LTE, needto be deployed with an increasing density of base stations. Thisdensification can be achieved by splitting macro cells and by deployingsmall cells in highly loaded geographical areas, or so called traffichotspots, within the coverage area of macro cells. With densification ofcellular networks, radio resources can be further reused and usersgenerally will be closer to their serving base stations, which enableshigher bitrates.

Cellular networks with a mixture of macro cells and small cells withoverlapping coverage areas are sometimes referred to as heterogeneousnetworks. These types of networks are seen as an important complement tomacro cell splitting. One example of such deployments is where clustersof pico cells are deployed within a macro coverage area to offload macrotraffic. A pico base station represents one example of a low power node,LPN, transmitting with low output power and correspondingly serving amuch smaller geographical area than a high power node, such as thetypical macro base station. Other examples of low power nodes are homebase stations and certain types of relays.

A consequence of network densification is that wireless devices, such asuser equipments (UEs), operating in the network will experience lowergeometries, which implies that downlink inter-cell interference can bemore pronounced and thus limit the achievable bit rates. Hence, in densecellular deployments, interference mitigation techniques have thepotential to substantially improve the user performance. Interferencemitigation can either take place on the transmitter side or on thereceiver side, or a combination of both. Interference mitigationtechniques often exploit the structure of the physical layertransmission used in the involved radio access technology.

Regarding receiver-side of techniques for mitigating inter-cellinterference, interference rejection combining or IRC is a well-knownreceiver type for suppressing interference. IRC processing requiresestimation of an interference/noise covariance matrix. Such matricesexpress the covariance of interference between the signals beingcombined via IRC processing. More advanced receiver types forinterference mitigation are based on interference cancelation or IC.With IC processing, unwanted received signals, e.g., intra/inter-cellinterference, are estimated and subtracted from the “overall” receivedsignal. In this regard, the overall received signal can be understood asbeing a composite of desired and undesired signals impinging on thereceiver antennas.

Maximum Likelihood, ML, is another interference mitigation technique.ML-type receivers recover transmitted symbol information from a receivedsignal based on jointly detecting symbol information from multiplesignals, e.g., from several different cells. The joint decision isdetermined based on minimizing a joint error metric. ML-type receiversusually rely on searching among all possible combinations of definedsymbol values, which are also referred to as modulation constellationpoints.

IRC and IC were established as UE reference receiver techniques inRelease 11 of the applicable LTE technical specifications by the ThirdGeneration Partnership Project, 3GPP. However, in LTE Release 11, alsoreferred to as Rel-11, IC was restricted to cancelation of always-onsignals, and the network assisted the UE as to how such signals weretransmitted in the aggressor cells. The Common Reference Symbols or CRS,which are transmitted in LTE networks on a cell-specific basis,represent one type of always-on signal for which IC-based interferencemitigation would be performed.

However, there is a growing interest in developing approaches for thecancelation and suppression of interference corresponding to schedulingof data, and such features are an item of interest in ongoing work forLTE Rel-12. Consequently, IC receivers in UEs for mitigating downlinkinterference arising from neighbor-cell data transmissions are nowgaining popularity. The IC receiver in the victim UE—i.e., the UEexperiencing the interference at issue—demodulates and optionallydecodes the interfering signals, and produces an estimate of thetransmitted and the corresponding received interfering signal. Thereceiver then removes that estimate from the overall or total receivedsignal, to improve the effective signal-to-noise-plus-interferenceratio, SINR, for the desired signal.

In post-decoding IC receivers, the interfering data signal isdemodulated and decoded. The decoding results and channel estimates forthe interfering signal are used to estimate the interfering signal'scontribution to the composite received signal—i.e., interfering signalas received by the IC receiver is regenerated from the decoding results.The regenerated signal is then removed from the composite receivedsignal, for improved demodulation and decoding of the desired signal orsignals from the composite received signal. Post-decoding IC receiversare sometimes referred to as Code-Word IC, CWIC, receivers.

As an alternative to post-decoding IC processing, pre-decoding ICreceivers perform the regeneration step directly after demodulation,thus bypassing the channel decoder with respect to the interferingsignal at issue. That is, a pre-decoding IC receiver performs symboldetection with respect to an interfering signal but does not provide thedetection results to its decoder. Instead, the detection results areused, e.g., in a “soft” symbol mapping process, to regenerate theinterfering signal, for removal from the composite received signal.Pre-decoding receivers are sometimes referred to as Symbol Level IC,SLIC, receivers.

The term cancelation efficiency or CE of an IC receiver denotes thefraction of impairment (interference plus noise) power remaining in thereceived signal, after the receiver performs cancelation processing. TheCE for the pre- and post-decoding IC approaches may be essentially equalin some scenarios and vary significantly in others. For example, thepost-decoding IC approach typically provides superior performance at“high” SINR operating points. The preferred approach is based onapplying soft signal mapping and regeneration, as opposed to using hardsymbol or bit decisions.

In many IC receiver architectures, as well as IRC and ML architectures,some prior knowledge about the interfering signal is required to performinterference mitigation or to enhance the performance of suchmitigation. Basic information includes knowledge about at least a subsetof the resource allocation of the interfering signal, modulation-relatedparameters of the interfering signal, and coding-related parameters ofthe interfering signal. For example, in LTE, resource allocationknowledge would mean knowing at least some of the Resource Blocks or RBsused for the interfering signal. In networks that use High-Speed PacketAccess, HSPA, the resources in question are codes used on the High-SpeedPhysical Downlink Shared Channel or HS-PDSCH. Example modulation-relatedparameters include transmission mode, modulation format,Multiple-Input-Multiple-Output, MIMO, rank, precoding weights, etc.Example coding-related parameters include transport block size, coderate, etc.

Receiving a neighbor-cell downlink, DL, control channel represents onemechanism for obtaining knowledge about interfering data transmissionsin the neighbor cell. More particularly, in advance of a neighbor-cellmaking a downlink data transmission to a given neighbor-cell UE, acontrol message is sent on the control channel of the neighbor cell.That control message carries resource allocation information, transportformat information, etc., for use by the targeted neighbor-cell UE inreceiving the upcoming data transmission.

In LTE, such a control channel is referred to as the Physical DownlinkControl Channel or PDCCH, while HSPA-based networks use a High SpeedShared Control Channel or HS-SCCH. Although the neighbor-cell controlchannel may be power-controlled towards the intended neighbor-cell UEand not toward the victim UE, in many scenarios of interest, the victimUE nonetheless experiences signal quality sufficient for decoding thecontrol message associated with the interfering signal. From this pointforward, the term “IC receiver” refers to a receiver that can mitigateneighboring cell interference. Examples of such receivers are IRC, ML,SLIC and CWIC.

In LTE, HSPA and other contemporary cellular networks, the DLtransmissions to UEs use fast link adaptation. In this scheme, a givenUE signals to its serving cell the channel quality experienced by the UEat the current scheduling interval, which for LTE is the currentsubframe and in HSPA is the current Transmission Time Interval or TTI.Here, it will be understood that the LTE subframe is functionally thesame as the HSPA TTI, in the sense that they both represent a basicscheduling interval. The UE further indicates the preferred rank andprecoding properties. The serving radio node (or base station or NodeB)receives this information and schedules a DL transmission severalsubframes or TTIs later using a transport format that the UE is able tosuccessfully decode, assuming the previously reported channel quality.Problematically, however, the interference properties at the current andfuture subframes or TTIs are different, and the achievable IC gain atthe UE for the future subframe or TTI is difficult to predict.

The difference between reception conditions as they exist at the UE whenthe scheduled transmission is later received and as they existed at theearlier reporting time often means that the CE of IC processing at theUE during reception of the scheduled transmission does not match the CEachievable at the time channel quality was reported. Fortunately, inpractical networks, the serving radio node usually applies some type ofadjustment to reported channel quality to obtain a desired long-termtarget Block Error Rate or BLER. This leads to more aggressive transportformat, TF, scheduling for IC-capable UEs, as compared to non-IC UEswith linear receivers, and it helps in the realization of averagethroughput, TP, gains and cell capacity gains from IC.

However, there are existing approaches directed to the mismatch betweenchannel quality as reported by a UE versus actual channel quality duringa later transmission to the UE. For example, an IC UE may predict thetransport format, TF, that will be used by a neighbor-cell base stationwhen making a transmission that will interfere with the UE's receptionof scheduled data. The UE then adjusts its current channel qualityreport in view of the predicted TF. That adjustment reflects thesensitivity of CE to the TF of interfering signals. Of course, theadjustment is imperfect in the sense that the prediction may be wrong.

In another approach, an IC UE reports own-cell channel quality andadditionally reports channel quality with respect to one or moreinterfering neighbor cells. The serving radio node uses the additionalinformation to better estimate what the channel quality will be at theUE during the later-scheduled transmission to the UE. Problematically,however, these approaches do not address the problem recognized herein.Namely, by not accounting for the actual TF of the interfering signalsat the UE at the actual time of transmission to the UE, the networkfails to realize the throughput and performance gains possible with ICUEs, by using link adaptations that are either too aggressive or notaggressive enough, which leads to reduced system capacity as aconsequence of not fully exploiting the channel capacity.

For example, overly aggressive TF selection causes an increasedincidence in retransmissions and hence uses more time-frequencyresources than necessary. On the other hand, if TF selection is tooconservative with respect to actual channel conditions at the UE duringthe transmission interval at issue, the UE is served at an effectiveSINR that is above what is needed for reliable decoding of thetransmitted data.

SUMMARY

According to one aspect of the teachings herein, network-side anddevice-side methods and apparatuses improve transmit link adaptation fordevices operating in a cellular communication network that haveinterference-canceling receivers. In particular, own-cell linkadaptation towards a given device in a current transmission intervaladvantageously exploits a determined mapping between theinterfering-signal cancelation efficiency of the device versusinterfering-signal transport format, in combination with actualknowledge of the transport format that will be used to make aninterfering neighbor-cell transmission in the current transmissioninterval.

An example embodiment is seen in a method of link adaptation toward awireless device, where a serving radio node in a cellular communicationnetwork performs the contemplated method. The method includesdetermining a mapping between interfering-signal transport formats andcorresponding interfering-signal cancelation efficiencies of the device,based on receiving interference-cancelation capability information fromthe device. Further, the method includes receiving an indication ofwhich transport format has been selected for use in a currenttransmission interval, for a neighbor-cell transmission that is expectedto be an interfering transmission with respect to an own-celltransmission to be made by the serving radio node towards the device inthe current transmission interval.

Still further, the method includes determining the interferencecancelation efficiency expected for the device with respect to theneighbor-cell transmission, as a function of the determined mapping andthe transport format known from the received indication.Correspondingly, the method additionally includes estimating theown-cell signal quality that will be experienced at the device in thecurrent transmission interval, as a function of the determinedcancelation efficiency and an own-cell channel quality value indicatedby the device in channel quality report received from the device in aprior transmission interval, and selecting the transport format to usefor the own-cell transmission as a function of the estimated own-cellquality.

An example serving radio node in the context of the above-describedmethod comprises a radio base station, such as a Node B or eNodeB in3GPP parlance. A base station in an example implementation includes aprocessing circuit that is configured to carry out processing operationsthat implement the above-described method. For example, the processingcircuit includes or is associated with a computer-readable medium, suchas FLASH or disk storage. In turn, the computer-readable medium stores acomputer program that includes program instructions which, when executedby the processing circuit, configure the radio node to determine themapping, determining the transport format that actually will be used foran interfering transmission, determining the cancelation efficiencyexpected for the device as a function of that known transport format,estimating the own-cell channel quality expected for the device as afunction of the determined cancelation efficiency, and selecting thetransport format to use for serving the device in the currenttransmission interval, as a function of the estimated own-cell channelquality.

Another embodiment comprises a method of channel quality reporting by awireless device having an interference-canceling receiver. The methodincludes sending interference-cancelation capability information to thenetwork, indicating one or more characteristics ofinterference-cancelation processing the device is configured to perform.Further, the method includes generating a channel quality report for aserving radio node in the network with respect to a current transmissioninterval.

The channel quality report is based on determining one or moreneighbor-cell channel quality values with respect to a neighbor celloriginating a neighbor-cell transmission that was detected by the deviceas an interfering transmission in the current transmission interval, anddetermining a set or range of serving-cell channel quality value versusdifferent interference cancelation efficiencies assumed for theinterfering transmission, or versus different transport formats assumedfor interfering transmission. The method further includes transmittingthe channel quality report to the serving radio node.

A wireless device in the context of the above-described device-sidemethod comprises, for example, a User Equipment or UE in 3GPP parlance.In an example implementation, the device includes a processing circuitthat is configured to carry out processing operations that implement theabove-described method. For example, the processing circuit includes oris associated with a computer-readable medium, such as FLASH or diskstorage. In turn, the computer-readable medium stores a computer programthat includes program instructions which, when executed by theprocessing circuit, configure the device to determine and reportown-cell and neighboring cell channel quality as described.

Of course, the present invention is not limited to the above featuresand advantages. Indeed, those skilled in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of a cellular communicationnetwork, including a radio node and a wireless device having aninterference-canceling receiver.

FIG. 2 is a block diagram of example implementation details with respectto the radio node and wireless device, as contemplated herein.

FIG. 3 is a logic flow diagram of one embodiment of a method of linkadaptation at a serving radio node, with respect to a wireless devicehaving an interference-canceling receiver.

FIG. 4 is a logic flow diagram of one embodiment of a method of channelquality reporting for link adaptation, as performed by a wireless devicehaving an interference-canceling receiver.

FIG. 5 is a signal flow diagram for one embodiment of link adaptationsignaling and associated network-side and device-side processing.

FIG. 6 is a signal flow diagram for another embodiment of linkadaptation signaling and associated network-side and device-sideprocessing.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of one embodiment of a cellular communicationnetwork 10 that is configured to provide service to a potentially largeplurality of wireless devices 12, where one such device 12 is shown forease of discussion. The device 12 is contemplated according to anexample embodiment and includes an interference-canceling, IC, receiver14, and a Channel Quality, CQ, reporting circuit 16.

As will be detailed, the interference-canceling receiver 14 achievesdifferent characteristic cancelation efficiencies with respect to agiven interfering signal, in dependence on the particular transportformat used for the interfering signal. Here, “transport format”connotes characteristic structure or format used for informationtransmission. In an LTE example, the transport format includes the blocksize used to transmit information, which in turn relates to theModulation-and-Coding-Scheme or MCS used to transmit the information andthe number of Physical Resource Blocks or PRBs allocated fortransmitting the information. The channel-quality reporting circuit 16is, in an example embodiment, configured to report own-cell channelquality as a function of different transport format assumptions for aninterfering neighbor-cell signal detected during the reporting interval.

Turning back to the diagram, the network 10 includes a number of cells18 having associated radio nodes 20, e.g., base stations such as Node Bsin an HSPA network and eNodeBs in an LTE network. Generally, a givendevice 12 will be “served” at any given time by one or more cells 18,referred to a “serving” cell 18. For example, the serving cell(s) 18make scheduled downlink transmissions 22 to the device 12. Reception ofthose own-cell transmissions 22 at the device 12 may be interfered withby one or more neighbor-cell transmissions 22, which are directed togiven devices 12 being served in those neighbor cells 18.

One sees an example scenario depicted in the diagram, wherein the cell18-1 is a serving cell 18 with respect to the device 12, and thedownlink transmissions 22-1 from the radio node 20-1 are potentiallyinterfered with by concurrent downlink transmissions 22 in one or moreneighboring cells 18. For example, the transmission 22-2 from the basestation 20-2 in the cell 18-2 may be an interfering transmission and/orone or both of the transmissions 22-3 and 22-4 from radio nodes 20-3 and20-4 in respective cells 18-3 and 18-4 may be interfering transmissions.Here, it will be understood that these interfering neighbor-celltransmissions 22-2, 22-3, and/or 22-4 may be directed to wirelessdevices 12 operating in their respective cells 18-2, 18-3, and 18-4, butfor clarity the diagram does not show these other users. Further, itwill be understood that with dynamic user scheduling, device mobilityand changing reception conditions, the particular neighbor cell 18 orcells 18 that are interfering may change.

There are common interference situations, however. For example, althoughthe drawing is not to scale, one sees in FIG. 1 that the network 10 isdepicted as a heterogeneous network in which different cells havedifferent sizes or coverage areas. Here, a “cell” may be understood asthe allocation of particular air interface resources—e.g., a givencarrier frequency or frequency subband—for providing radio service in acorresponding geographic region, area or location. In a knownheterogeneous network arrangement, a large or macro cell 18 (18-2 inFIG. 1) is overlaid by one or more small or pico cells 18 (18-1, 18-3and 18-4 in FIG. 1). The pico cells 18 are used to fill in coverage gapsin the macro cell area, to extend the capacity of the network 10 in themacro cell area, and/or to provide higher data rate “hotspot” coveragewithin the macro cell area.

In such heterogeneous arrangements, it is common for a device 12 beingserved by a pico cell 18 to experience potentially significant downlinkinterference from the associated macro cell. In the diagram, forexample, the radio node 20-1 may be assumed to be the serving radionode, meaning that own-cell transmissions 22-1 from the radio node 20-1towards the device 12 operating in the pico cell 18-1 may experiencesignificant interference arising from overlapping neighbor-celltransmissions by the radio node 20-2 towards another device 12 beingserved in the macro cell 18-2. Such interference becomes especiallyproblematic as the device 12 moves towards the boundary area of the picocell 18-1, where the device 12 may see a relatively high channel qualitytowards the interfering neighbor cell 18-2.

Of course, the device 12 may experience interference from one or more ofthe other pico cells 18-3 and 18-4. Moreover, even in embodiments of thenetwork 10 that use homogeneous cell and radio node arrangements, e.g.,embodiments that use more uniformly sized cells 18 and radio nodes 20 ofcomparable transmit power, the device 12 may experience interferingtransmission 22 from one or more neighbor cells 18, while operating in agiven serving cell 18.

With these points in mind, one or more of the radio nodes 20 in thenetwork 10 are configured according to the teachings herein, to therebyprovide improved link adaptation towards devices 12 havinginterference-canceling receivers 14. In an example arrangement asillustrated by FIG. 2, the contemplated radio node 20 includes a linkadaptation circuit 24, which may be encompassed in a user schedulingcircuit, for adapting the transmission link according to the teachingsherein, a channel quality synthesis circuit 26, for estimating channelquality according to the teachings herein, and a channel qualityreporting control circuit 28, for controlling channel quality reportingby devices 12 according to the teachings herein.

FIG. 2 illustrates more details for an example radio node 20 and anexample device 12. The illustrated radio node 20 is configured foroperation in a cellular communication network 10 as a serving radio nodewith respect to a wireless device 12, and it comprises a first signalinginterface 32 that is configured to receive transport format selectioninformation, and a second signaling interface 42 that is configured tosend signaling to the wireless device 12 and to receive signaling fromthe wireless device 12. The node 20 further includes a processingcircuit 34 that is operatively associated with the first and secondsignaling interfaces 32 and 42 and configured to perform link adaptationtowards the device 12.

The processing circuit 34 is configured to determine a mapping betweeninterfering-signal transport formats and correspondinginterfering-signal cancelation efficiencies of the device 12, based oninterference-cancelation capability information received from the device12, and to receive, via the first signaling interface 32, an indicationof which transport format has been selected for use in a currenttransmission interval, for a neighbor-cell transmission that is expectedto be an interfering transmission with respect to an own-celltransmission to be made by the serving radio node 20 towards the device12 in the current transmission interval. The interference-capabilityinformation may be received via the second signaling interface 42, whichin one or more embodiments comprises a wireless communication interface,e.g., cellular radio circuitry for transmitting downlink signals andreceiving uplink signals.

The processing circuit 34 is further configured to determine theinterference cancelation efficiency expected for the device 12 withrespect to the neighbor-cell transmission, as a function of thedetermined mapping and the transport format known from the receivedindication, and to estimate the own-cell signal quality that will beexperienced at the device 12 in the current transmission interval, as afunction of the determined cancelation efficiency and an own-cellchannel quality value indicated by the device 12 in the channel qualityreport received from the device 12 in a prior transmission interval.Still further, the processing circuit 34 is configured to select thetransport format to use for the own-cell transmission as a function ofthe estimated own-cell quality. In this manner, the linkadaptation—e.g., the selection of a specific transport format to use forthe own-cell transmission in the current transmission interval—is basedon knowledge of the actual transport format that will be used to performthe interfering transmission.

In one embodiment, the radio node 20 controls or otherwise coordinatesthe neighbor-cell transmission, and the first signaling interface 32 isan internal interface implemented within the processing circuit 34. Byway of non-limiting example, an internal interface can be a logicalsignaling interface between processing routines or functions beingcarried out in common by a given digital signal processor or otherdigital processing circuit, or it can be a physical signaling betweendifferent processing devices, e.g., on a backplane or other circuitboard within the radio node 20.

In another embodiment, the radio node 20 does not control or otherwisecoordinate the neighbor-cell transmission, and the first signalinginterface 32 is an external interface coupling the radio node 20 toanother node 20 in the network 10 having knowledge of the transportformat that has been selected for the neighbor-cell transmission. In anLTE embodiment, for example, where the radio node 20 comprises aneNodeB, the first signaling interface 32 comprises an X2 interface toone or more neighboring eNodeBs. More broadly, the first signalinginterface 32 in such embodiments is an inter-base-station or otherinter-node communication interface that communicatively couples theradio node 20 to another, external node in the network 10 that hasknowledge of the transport format that will be used for the interferingtransmission.

As will be appreciated, the processing circuit 34 comprises one or morephysical or functional circuits, and it may be realized using fixedcircuit elements, programmed processing circuits, or some combination ofboth. In at least one embodiment, the processing circuit 34 isprogrammatically configured as a specially-adapted machine for carryingout the network-side operations taught herein, for link adaptation withrespect to devices 12 having interference-canceling receivers 14. Forexample, the computer program 38 may be a computer program productstored in the memory/storage 36, which storage may be FLASH, diskstorage, or some other computer-readable medium providing persistentstorage of the computer program 38.

The computer program 38 comprises program instructions that whenexecuted by the processing circuit 34 configured the processing circuit34 to carry out the example method 300 illustrated in FIG. 3. Of course,it is contemplated that the processing circuit 34 can be configured toimplement variations of the method 300, through programmatic changesand/or changes to fixed circuitry.

In any case, the method 300 is a method of link adaptation toward awireless device 12 by a serving radio node 20 in a cellularcommunication network 10 and the method includes determining (Block 302)a mapping between interfering-signal transport formats and correspondinginterfering-signal cancelation efficiencies of the device 12, based onreceiving interference-cancelation capability information from thedevice 12. The interference-cancelation capability information maydirectly indicate the cancelation capabilities of the device 12 fordifferent transport formats, e.g., for a number of defined transportformats. In other embodiments, the interference-cancelation capabilityinformation simply identifies the type interference-canceling receiver14 that is implemented by the device 12 and the node 20 relates this toa table or other data structure that maps the cancelation efficiency todifferent possible transport formats.

For example, the mapping information 40 may comprise look-up tables thatprovide such a mapping for different types or grades ofinterference-canceling receivers 14. Consider that in one embodiment,the device 12 is configured to send interference-cancelation capabilityinformation comprising an indication as to whether the device 12 isconfigured to perform pre-decoding interference cancelation orpost-decoding interference cancelation. On the network side in suchembodiments, the mapping information 40 comprises one or more look-uptables for pre-decoding types of interference-canceling receivers andone or more look-up tables for post-decoding types ofinterference-canceling receivers.

Further, the mapping information may be multi-dimensional. That is, insome embodiments, the mapping is one-dimensional, where the expectedinterference cancelation efficiency of the interference-cancelingreceiver 14 of the device 12 is expressed solely as a function of thetransport format of the interfering signal to be canceled. In otherembodiments, the mapping information is multi-dimensional, e.g., mappingis performed as a function of the transport format of the interferingsignal to be canceled, and further as a function of channel quality atthe device 12 with respect to the interfering signal. In one suchembodiment, the mapping information comprises, for a given type ofinterference-canceling receiver 14, two or more tables, each one mappingdifferent transport formats to different cancelation efficiencies, for acorresponding interfering-signal quality or range of signal quality.

There may be a set of such tables for each characterized type ofinterference-canceling receiver 14. Moreover, those of skill in the artwill appreciate that the tables for a given receiver type can beconsolidated into a multi-dimensional table or matrix, which is indexedby interfering-signal channel quality and interfering-signal transportformat.

In any case, the method 300 further includes receiving (Block 304) anindication of which transport format has been selected for use in acurrent transmission interval, for a neighbor-cell transmission that isexpected to be an interfering transmission with respect to an own-celltransmission to be made by the serving radio node 20 towards the device12 in the current transmission interval. That is, by virtue of obtainingthis indication, the radio node 20 definitively knows the actualtransport format that will be used to make the interfering transmissionand, in turn, the method 300 includes determining (Block 306) theinterference cancelation efficiency expected for the device 12 withrespect to the neighbor-cell transmission, as a function of thedetermined mapping and the transport format known from the receivedindication.

In an example case, the known transport format will match one of thetransport formats that is an entry or data point within the determinedmapping. For example, assume that the determined mapping expresses thecancelation efficiency as a function of five different possibletransport formats. If the known transport format matches one of those,then the cancelation efficiency corresponding to that matched transportformat entry is taken to be the cancelation efficiency that the device12 is expected to achieve in the current transmission interval withrespect to interfering signal. If the known transport format does notmatch any of the transport format entries in the determined mapping,then the cancelation efficiency can be determined by interpolatingbetween the two closest-matching transport formats in the determinedmapping—e.g., the two transport format entries that bracket the knowntransport format in terms of block size parameters, MCS, etc.

In turn, the method 300 further includes estimating (Block 308) theown-cell signal quality that will be experienced at the device 12 in thecurrent transmission interval, as a function of the determinedcancelation efficiency and an own-cell channel quality value indicatedby the device 12 in channel quality report received from the device 12in a prior transmission interval. Still further, the method 300 includesselecting (Block 310) the transport format to use for the own-celltransmission as a function of the estimated own-cell quality.

With respect to the above processing, the “prior” transmission intervalmay be the immediately prior transmission interval, or may be earlierthan the immediately prior transmission interval. Further, the channelquality at issue may be averaged over more than one prior transmissioninterval. Here, a “transmission interval” generally comprises the unitof time used defined by the network 10 for making scheduling decisions.In an HSPA embodiment example, the transmission interval is oneTransmission Time Interval or TTI, which comprises one subframe of twomilliseconds duration, and where five subframes comprise an overallframe. In an LTE embodiment example, the transmission interval is onesubframe of one millisecond duration, where ten subframes comprise anoverall frame.

Thus, for adapting the transmission link, for making an own-celltransmission to served device 12 in the current transmission interval,the radio node 20 obtains exact knowledge of the transport format thatwill be used by a neighbor-cell 18 in making a neighbor-celltransmission that is expected to interfere with the own-celltransmission. Here, the neighbor-cell transmission is expected tointerfere, based on the device 12 previously reporting the neighbor-cell18 as an interfering cell. Thus, the radio node 20 uses the knowntransport format and the determined mapping information to accuratelyestimate the cancelation efficiency that the device 12 is expected toachieve with respect to the interfering transmission, and to use thataccurately estimated cancelation efficiency along with previouslyreported own-cell channel quality information, to accurately estimatethe actual own-cell post-IC channel quality that the device 12 willexperience with respect to the own-cell transmission in the currenttransmission interval.

In some embodiments, the channel quality report received from the device12 in the prior transmission interval indicates neighbor-cell channelquality values for more than one neighbor cell 18, as determined by thedevice 12 for the neighbor cells 18 in the prior transmission interval,and further indicates a set or range of own-cell channel quality values,as determined by the device 12 for the prior transmission interval, fora corresponding set or range of assumed cancelation efficiencies withrespect to each such neighbor cell 18.

In such embodiments, the processing circuit 34 is configured to use thereported neighbor-cell channel quality values as an extra dimension indetermining the cancelation efficiency expected for the device 12 in thecurrent transmission interval with respect to the interferingtransmission to be made by the neighbor cells 18 for which the channelquality values were reported. That is, the radio node 20 is configuredto consider the neighbor-cell channel quality reported by the device 12in a prior transmission interval as well as the neighbor-cell transportformat known for the current transmission interval, to determine thecancellation efficiency expected at the device 12 with respect to theneighbor cell 18 in the current transmission interval.

Such processing reflects the fact that the cancelation efficiency of thedevice 12 with respect to a given interfering neighbor-cell transmissiondepends on the channel quality of the interfering transmission, inaddition to depending on the transport format of the interferingtransmission. Thus, determining (Block 306) the interference cancelationefficiency expected for the device 12 with respect to givenneighbor-cell transmissions in the current transmission interval furtheris a function of the channel quality values indicated for the givenneighbor cells 18 in the prior channel quality report.

In at least one embodiment, estimating (Block 308) the own-cell signalquality that will be experienced at the device 12 in the currenttransmission interval comprises selecting the own-cell channel qualityvalue in the indicated set or range of own-cell channel quality valuescorresponding to the assumed cancelation efficiency that matches thedetermined cancelation efficiency. Alternatively, the estimationcomprises interpolating between the two-own-cell channel quality valuesin the indicated set or range of own-cell channel quality values thatcorrespond to the two assumed cancelation efficiencies bracketing thedetermined cancelation efficiency.

In some embodiments, in advance of receiving the channel quality reportfrom the device 12 in the prior transmission interval, the method 300further includes receiving an indication of interferer cells 18 detectedby the device 12, including detection of the neighbor cell 18 as aninterfering cell 18, and further includes identifying the neighbor cell18 as being an interferer cell 18 of interest among one or moreinterferer cells 18 so identified by the device 12, and sending a returnindication of the one or more interferer cells 18 of interest to thedevice 12. Thus, in some embodiments, the device 12 identifies theneighboring cells 18 that are interfering cells 18 and the radio node 20indicates to the device 12 which ones of the interfering cells 18 shouldbe reported on in the channel quality reports sent by the device 12.That is, the radio node 20 tells the device 18 for which interferingneighbor cells 18 to report channel quality. The radio node 20 mayelect, for example, to have the device 12 report for only thestrongest—dominant—interfering neighbor cell 18, or to report for thetwo strongest, three strongest, etc., neighbor cells 18. Alternatively,the radio node may have the device 12 report for specific interferingneighbor cells 18, based on the radio node 20 having advance knowledgeof which neighbor cells 18 will be scheduled in a future transmissioninterval. Then, when that future transmission interval becomes thecurrent transmission interval, the device 12 will have reported channelquality with respect to the neighbor cells 18 that will make a scheduledtransmission in the current transmission interval.

Thus, according to some embodiments of the method 300, there may be twoor more neighbor-cell transmissions that are expected to be interferingtransmissions with respect to an own-cell transmission to be made by theserving radio node 20 towards the device 12 in the current transmissioninterval. Correspondingly, the step of receiving (Block 304) includesreceiving indications of which transport formats have been selected forthe interfering transmissions, the step of determining (Block 306)includes determining the cancelation efficiencies expected for thedevice 12 with respect to the interfering transmissions, and the step ofestimating (Block 308) includes estimating the own-cell signal qualitythat will be experienced at the device 12 in the current transmissioninterval as a function of the determined cancelation efficiencies andthe own-cell channel quality reported by the device 12 in the priortransmission interval.

Further, in some embodiments of the method 300, the channel qualityreport indicates a set or range of own-cell channel quality values, asdetermined by the wireless device 12 in the prior transmission intervalfor a set or range of assumed interfering-signal transport formats.Here, the step of estimating (Block 308) the own-cell signal qualitycomprises selecting the own-cell channel quality value from theindicated set or range that corresponds to the assumedinterfering-signal transport format matching the transport format knownfrom the received indication, or interpolating between the two own-cellchannel quality values that correspond to assumed interfering signaltransport formats that bracket the transport format known from thereceived indication.

Additionally, in some embodiments of the method 300, the method includesobtaining in one or more transmission intervals previous to the currenttransmission interval, indications of which transport formats were usedfor neighbor-cell transmissions from one or more neighbor cells 18,which were detected as interfering transmissions with respect toprevious own-cell transmissions to the device 12. Knowledge of theactual transport formats used for past interfering transmissions can beused in determining (Block 302) the mapping between interfering-signaltransport formats and corresponding interfering-signal cancelationefficiencies of the device 12. For example, the incidence of ACKs versusNACKs received for prior downlink transmissions can be used to infer thecancelation efficiencies being achieved at the device 12 with respect topast own-cell transmissions towards the device 12, where the transportformat(s) of the interfering neighbor-cell transmission(s) during thosepast own-cell transmissions are known from the obtained indications.Thus, the radio node 20 correlates the incidence of ACKs and NACKs withthe known interfering-signal transport formats and deduces or refinesthe interference cancelation efficiency of the device 12 for differentinterfering-signal transport formats.

Even in embodiments where the radio node 20 receives or is preconfiguredwith mapping information indicating the cancelation efficiency of thedevice's interference-canceling receiver 14 with respect differentinterfering-signal transport formats, the above ACK/NACK correlationprocessing can be used over time to refine or otherwise revise thetable. Such an approach allows the radio node 20 to begin with a defaulttable, which may not be fully particularized with respect to a giveninterference-canceling receiver 14 in a given device 12, and then refinethat table over time.

With respect to the above processing, the channel quality synthesiscircuit 26 in one or more embodiments is configured to perform theprocessing operations represented by Blocks 302, 304, 306, and 308, forexample, while the link adaptation/scheduling circuit 24 is configuredto perform the processing operations represented by Block 310. Further,the channel quality reporting control circuit 28 is configured toidentify the neighbor cells 18 which are interferer cells 18 ofinterest, with respect to channel quality reporting by the device 12.That is, the channel quality reporting control circuit 28 may beconfigured to monitor which neighbor cells 18 are reported by the device12 as interfering cells 18, to select the dominant one or most-dominantones of those cells 18 as interferer cells 18 of interest, and to sendindications of such to the device 12, to cause the device 12 to provideneighbor-cell channel quality reporting for the selected interferercells 18.

Turning back to FIG. 2, the example device 12 comprises one or moretransmit/receive antennas 50 and an associated signaling interface 52that is configured to send signals to the network 10 and receive signalsfrom the network 10. For example, the signaling interface 52 comprises awireless communication transceiver having a radio receiver and a radiotransmitter configured for operation in the cellular communicationnetwork 10.

The device 12 further comprises a processing circuit 54 that isoperatively associated with the signaling interface 52. The processingcircuit 54 is configured to send interference-cancelation capabilityinformation to the network 10, indicating one or more characteristics ofinterference-cancelation processing the device 12 is configured toperform. The processing circuit 54 is further configured to generate achannel quality report for a serving radio node 20 in the network 10with respect to a current transmission interval. In this regard, theprocessing circuit 54 is configured to determine one or moreneighbor-cell channel quality values with respect to a neighbor cell 18that that was detected by the device 12 as making an interferingtransmission in the current transmission interval.

Still further, the processing circuit 54 is configured to determine aset or range of serving-cell channel quality values versus differentinterference cancelation efficiencies assumed for the interferingtransmission, or versus different transport formats assumed forinterfering transmission, and transmit the channel quality report to theserving radio node 20 via the signaling interface 52. Here, it will beunderstood that the interference cancelation efficiency of the device 12with respect to the interfering transmission depends on the transportformat used by the neighbor cell for the interfering transmission.

With respect to the above processing configuration, the processingcircuit 54 functionally or physically comprises the aforementionedinterference-canceling receiver 14 and the channel quality reportingcircuit 16. The processing circuit 54 further comprises or is associatedwith memory/storage 56, such as FLASH, EEPROM, or other solid-state ordisk-based storage, and the device 12 may further include additionalprocessing circuitry 62, such as user interface circuitry,application-level processing circuitry, etc., in accordance with theintended use and feature set of the device 12.

In one or more embodiments, the memory/storage 56 stores a computerprogram 58 and mapping information 60. The mapping information 60 maysimply comprise an indication of the type of interference-cancelingreceiver 14 implemented by the device 12, which can be then used by theradio node 20 to determine the mapping between the interfering-signalcancelation efficiency of the interference-cancelation receiver 14 andthe transport format of an interfering signal being canceled.Alternatively, the mapping information 60 may comprise a look-up tableor other data structure that gives characteristic cancelationefficiencies for a range or set of defined transport formats—e.g., for anumber of different transport formats that are known for use in thenetwork 10.

The processing circuit 54 may comprise fixed circuitry, programmedcircuitry, or some combination of both. In one or more embodiments, theprocessing circuit 54 is specially adapted to carry out the device-sideprocessing contemplated herein, based on its execution of the programinstructions comprising the computer program 58 stored in thememory/storage 56. In that regard, the memory/storage 56 will beunderstood as including some type of computer-readable medium thatprovides persistent data storage for the computer program 58.

In an example case, the computer program 58 comprises programinstructions that, when executed by the processing circuit 54, configurethe processing circuit 54 to carry out the method 400 illustrated inFIG. 4. The method 400 provides for channel quality reporting by awireless device 12 configured for operation in a cellular communicationnetwork 10, and includes sending (Block 402) interference-cancelationcapability information to the network 10, indicating one or morecharacteristics of interference-cancelation processing the device 12 isconfigured to perform. The characteristics may be indicated by sending,e.g., a receiver type indication or by sending mapping informationcharacterizing the interference cancelation efficiency of theinterference-canceling receiver 14 of the device 12 for a range ofinterfering-signal transport formats and, optionally, differentinterfering-signal channel qualities.

The method 400 further includes generating (Block 404) a channel qualityreport for a serving radio node 20 in the network 10 with respect to acurrent transmission interval. It will be understood that this step mayfollow Step 402 some indeterminate time later, and that Step 402 may,for example, be done once with respect to any given serving cell 18,while Steps 404 and 406 are repeated every transmission interval, or onan otherwise frequent basis.

In any case, in some embodiments, Block 404 includes determining (Block404A) one or more neighbor-cell channel quality values with respect to aneighbor cell 18 originating a neighbor-cell transmission that wasdetected by the device 12 as an interfering transmission in the currenttransmission interval, and determining (Block 404B) a set or range ofserving-cell channel quality values versus different interferencecancelation efficiencies assumed for the interfering transmission, orversus different transport formats assumed for interfering transmission.As noted, the interference cancelation efficiency of the device 12 withrespect to the interfering transmission depends on the transport formatused by the neighbor cell 18 for the interfering transmission.

The method 400 further includes transmitting (Block 406) the channelquality report to the serving radio node 20. The channel quality reportis sent for the current transmission interval from the perspective ofthe device 12, but it is used by the radio node 20 at a latertransmission interval that, from the perspective of the radio node 20 isthen the current transmission interval. For example, in a firsttransmission interval, the device 12 sends a channel quality report tothe radio node 20, based on measurements and estimations performed bythe device 12 for the first transmission interval, and then in a latersecond transmission interval, the radio node 20 extrapolates,interpolates, or otherwise determines the own-cell channel qualitytowards the device 12, as expected in the second transmission interval,based on the values reported for the first transmission interval.

In some embodiments, the method 400 includes identifying the neighborcell 18 or cells 18 for inclusion in the channel quality report basedon: identifying one or more neighbor cells 18, including aforementionedneighbor cell 18, as interfering neighbor cells 18, sending anindication of the interfering neighbor cells 18 to the serving radionode 20, and receiving a return indication identifying the neighbor cell18 as an interferer cell 18 of interest to include in channel qualityreporting. In at least one such embodiment, the method 400 includessending an updated indication to the network 10 from time to time, as towhich neighboring cells 18 are seen as interfering cells 18 by thedevice 12. In turn, the radio node 20 may send updated indications tothe device 12, as to which neighbor cells 18 are interferer cells 18 ofinterest.

With the above network-side and device-side processing in mind, it willbe understood that a serving radio node 20 as contemplated hereinobtains actual knowledge of the transport format that will be used foran interfering transmission during a current transmission interval, anduses the known transport format to more accurately estimate thecancelation efficiency that will be achieved by theinterference-canceling receiver 14 of a device 12, with respect to theinterfering transmission. Here, the cancelation efficiency of theinterference-canceling receiver 14 is a function of interfering-signaltransport format, and is known to the radio node according to a mappingbetween cancelation efficiency and transport format determined for thedevice 12.

In turn, the more accurate estimation of cancelation efficiency is usedto obtain a more accurate estimate of the own-cell channel quality thatwill be experienced by the device 12 for an own-cell transmissiontowards the device during the current transmission interval. Forexample, an own-cell channel quality estimate made by the device 12 in aprior transmission interval is adapted, transformed or otherwise usedwith the more accurate estimate of cancelation efficiency to derive amore accurate estimate of the actual, post-cancelation signal qualitythat the device 12 will experience in the current transmission intervalwith respect to the own-cell transmission. Here, it is safely assumedthat the channel conditions from the prior interval are generally stillapplicable to the current transmission interval. In some embodiments,channel quality averaging over two or more intervals may be used tofilter such values.

In a particular example, the interference cancelation efficiency of thedevice 12 with respect to an interfering neighbor-cell transmissiondepends in a characteristic, known manner on the actual transport formatused by the neighbor cell for the interfering transmission. As thedevice generally does not have actual knowledge of the transport formatused for the interfering transmission, it parameterizes its own-cellchannel quality directly or indirectly as a function ofinterfering-signal transport format, for a range or set of definedtransport formats. That is, in a given transmission interval, the device12 measures own-cell channel quality on a pre-cancelation basis and thenderives what its post-cancelation own-cell channel quality would be fora range or set of assumed interfering-signal transport formats.

The device 12 sends this set or range of own-cell channel quality valuesto the radio node 20. Then, in a subsequent transmission interval, theradio node 20 obtains an indication of the actual transport format thatwill be used for a neighbor-cell transmission that is expected tointerfere with an own-cell transmission to be made towards the device 12in that subsequent transmission interval. It advantageously uses thatknown transport format and the previously reported set or range ofown-cell channel quality values to identify or derive the own-cellchannel quality expected for the device 12 in this subsequenttransmission interval. This improved estimation also may incorporateconsideration of the dependency of interference cancelation efficiencyat the device 12 on neighbor-cell channel quality.

With the above in mind it will be appreciated that a first aspect of theteachings herein involved signaling from the device 12 to the network10. It is contemplated that a device 12 signals one or morecharacteristics or parameters of its interference-canceling receiver 14.For example, the device 12 may signal its interference-cancelationcapability class, such as pre-decoding configuration, post-decodingconfiguration, its capabilities for common and control channelinterference cancelation, its interference-cancelation adaptivity orinterference cancelation quality parameters, etc.

Such signaling is sent to the network 10 by the device 12 at connectiontime, e.g., using higher-layer signaling. The network 10 may have anominal cancelation efficiency map for each class or type ofinterference-canceling receiver 14. Mapping information for thedifferent types or classes receivers is stored, for example, as themapping information 40 in the memory/storage 36 of given radio nodes 20.

Alternatively, the device 12 transmits its actual cancelation-efficiencymapping table comprising, e.g., a set of cancelation efficienciescorresponding to different interfering-signal transport formats. Yetanother alternative is that the device 12 transmits its cancelationefficiency relative to a standardized CE mapping table, wherein therelative mapping can be limited to some few values or constitute acomplete mapping table. In one embodiment, the transmitted mapping tablemay consist of cancelation efficiency values for a fixed or customsampling of interfering-signal transport formats and interfering-signalSINR values. Cancelation efficiency values for transport format and SINRvalues not represented in the table are found by interpolating betweenthe table entries.

Further, a radio node 20 can remap the cancelation efficiency values forthe reported transport formats to cancelation efficiency valuescorresponding to actual transports used for the interferingtransmissions of interest. Small mismatches between the assumed andactual cancelation efficiency have only a limited performance impact.Note, too, that some devices 12 may transmit full cancelation-efficiencymapping tables, while other devices 12 transmit only receiver type orclass information, and rely on the network 10 to determine thecorresponding cancelation-efficiency mapping table as pre-stored in thenetwork 10.

Another aspect of the teachings herein relates to the signaling ofsignificant interferers. At infrequent intervals, e.g., at intervalsmuch longer than one TTI or whatever the basis transmission interval isdefined as, or at the request of the network 10, a given device 12signals to the network 10 a list of significant potential interferingcells 18. For example, the device 12 sends a list of cell IDs, CIDs, forthe neighbor cells 18 having the strongest signals towards the device12. The strongest cells 18 can be detected by the device 12 using CRSpower measurements on the received neighbor-cell signals.

In turn, the serving radio node 20 of the device 12 is configured tosend a list of interferer cells 18 of interest to the device 12, fromtime to time. The sending interval may be on a per transmissioninterval, or may be longer. The interferer cells 18 of interest areidentified by the serving radio node 20 as, for example, theintersection between the set of neighbor cells 18 that the device 12 hasidentified as interfering cells 18 and the set of neighbor cells 18 thathave been or will be scheduled for data transmissions in a futuretransmission interval or intervals.

In at least one particular scenario, the set of interferer cells 18 ofinterest may devolve into a single interferer cell 18 of interest. Forexample, consider the case where the device 12 is served by a pico cell18-1 that overlays a portion of a macro cell 18-2. In such cases,downlink transmissions originating in the macro cell 18-2 often dominatethe interference seen by the device 12 with respect to own-cell downlinktransmissions from the pico cell 18-2 to the device 12. More generally,in scenarios where the device 12 is served by a low-power radio node 20and operates in a range extension region, the associated macro celltransmissions represent the only significant interfering transmission.In such cases, the signaling between the device 12 and the low-powerradio node 20 regarding the list of interfering cells 18 from the device12 to the node 20, and the list of interferer cells 18 of interest fromthe node 20 to the device 12, may be skipped.

In another, related aspect of the teachings herein, the device 12 may beconfigured to expand its channel quality reporting, so thatneighbor-cell channel quality is reported in addition to own-cellchannel quality, at least for the interferer cells 18 of interest, asidentified by the device 12 and/or by the network 10.

In one such embodiment, at intervals faster than fading changes,possibly at each transmission interval, the device 12 reports channelquality values for the serving cell 18 and for one or more interferercells 18. Here, a channel quality value can be a Channel QualityIndicator or CQI value, or can be an SINR measurement, or can be anotherdefined value representing Channel State Information or CSI with respectto the corresponding cell 18. The channel quality report sent by thedevice 12 in a given current transmission interval generally is validfor that transmission interval and may be assumed to remain valid foruse by the serving radio node 20 in a future transmission interval, atleast in terms of the basic channel quality estimates.

For example, in a given current transmission interval from the servingradio node's perspective, the pre-cancelation own-cell channel qualityreported by the device 12 in a prior transmission interval provides avalid basis for estimating what the post-cancelation channel qualitywill be for the device 12 in the current transmission interval,according to the known transport format(s) to be used for theinterfering neighbor-cell transmissions to be made in the currenttransmission interval.

The information included in a given channel quality report by the device12 can be varied, as will be appreciated by those of ordinary skill inthe art. However, in some embodiments herein, it includes one or moreown-cell channel quality values representing estimated or measuredchannel quality with respect to own-cell transmissions from the servingradio node 20, and one or more neighbor-cell channel quality valuesrepresenting estimated or measured channel quality with respect to oneor more interfering neighbor-cell transmissions.

The reported information thus may assume many possible forms andincludes one or more of the following parameters: own-cell channelquality, e.g., CSI, without interference cancelation, own-cell channelquality, e.g., CSI, with interference cancelation on all interferingcells 18 being addressed via interference-cancelation processing at thedevice 12, own-cell channel quality with interference cancelationaccording to current interfering transport format on one interferingcell 18 at a time, own-cell channel quality with modeled full removal ofone interfering cell 18 at a time, channel quality values for individualinterfering cells 18, and an own-cell channel quality table fordifferent interfering cells 18 at different cancelation efficiencieswith respect to each interfering cell 18, e.g., an N-dimensional tablefor N interferer cells 18 of interest.

In some simplified embodiments, which are particularly well suited forlow mobility or semi-static scenarios, the channel quality reportingwith respect to interfering cells 18 may be omitted. In turn, the radionode 20 may be configured to evaluate the signal strength or SIRmeasurement reports from the device 12 to assess the interfering linkchannel quality.

Regardless of the channel quality reporting implementation, a notableaspect of the teachings herein involves the estimation by the network10, e.g., by the relevant serving node 20, of the own-cell channelquality that is expected at the device 12 for a current transmissioninterval in which an own-cell transmission will be made towards thedevice 12, and for which the actual transport format is known for aneighbor-cell transmission that is expected to be an interferingtransmission with respect to the own-cell transmission. Of course, theestimation may account for multiple interfering transmissions in view oftheir known transport formats and the cancelation efficienciescorrespondingly expected for them at the device 12, based on thedetermined mappings between interfering-signal transport format andinterference cancelation efficiency at the device 12.

In an example operation, during each transmission interval, the linkadaptation/scheduling circuit 24 at a given radio node 20 uses channelquality information previously derived or received from a served device12, in combination with the scheduling information known with respect tointerfering signals in the past and current transmission intervals, toaccurately estimate the effective own-cell channel quality of the device12 in the current transmission interval. This more accurate estimationcan be understood as a “synthesizing” the effective own-cell channelquality of the device 12 for the current transmission interval, based onactual knowledge of interfering signal transport formats at issue in thecurrent and past transmission intervals. The more accurate channelquality estimation is then used by the radio node 20 to determine thepreferred transmission settings for the own-cell transmission to thedevice 12 in the current transmission interval, including selection ofthe most aggressive transport format that can be used in view of themore accurately estimated effective own-cell channel quality. Here, themost “aggressive” transport format is the one that transmits the mostbits while still meeting any applicable decoding reliability targets,e.g., a decoding probability of ninety-percent.

In at least some embodiments contemplated for the linkadaptation/scheduling circuit 24 of a serving radio node 20, the circuit24 uses previously reported channel quality information from a serveddevice 12, along with knowledge of the transport formats used for therelevant interfering signals in the past and the current transmissioninterval, to synthesize an accurate estimate of the effective own-cellchannel quality at the served device 12. The effective own-cell channelquality is then used to select the preferred transmission settings forthe own-cell transmission to the served device 12 in the currenttransmission interval, including the scheduling of an appropriatetransport format. Transport format selection here can be moreaggressive, because the interference cancelation performance to beachieved by the device 12 in the current transmission interval is moreaccurately known as a consequence of the radio node 20 having actualknowledge of the relevant interfering signal transport formats.

The radio node 20 may obtain channel quality for each interferer cell 18of interest at the victim device 12 based on conventional, legacymethods. In another approach, channel quality for the own cell withoutconsidering interference cancelation is computed using legacy methodsknown for linear, non-IC receivers. Channel quality for the own cellassuming full interference cancelation can then be computed for acertain neighbor cell 18 by computing the signal or impairmentcovariance matrix for the linear receiver, subtracting a parametricallyconstructed covariance correction term for the interferer, and computingchannel quality using the corrected covariance matrix. The differencebetween the channel quality values thus computed for each interferergives an estimate of channel quality for that interferer.

In another option, channel quality for the own cell is computed withoutconsidering the effect of interference cancelation, using legacy methodsknown for linear, non-IC receivers. Channel quality for the own cell isthen computed in consideration of interference cancelation as performedon a selected one of the interferer cells 18 of interest, based onevaluating the actual post-IC symbol SINR seen at the device 12. Becausethe radio node 20 knows the actual transport format that was used forthat interferer cell transmission, and knows the characteristiccancelation efficiency of the device's interference-canceling receiver14 for that transport format, it can compute the relevant neighbor-cellchannel quality.

The radio node 20 next uses one or more items of information to obtaincancelation efficiency estimates for one or more the interferer cells 18of interest with respect to the current transmission interval. Forexample, the radio node 18 bases the cancelation efficiency estimate onthe determined mapping between cancelation efficiency andinterfering-signal transport format. Additionally, the cancelationefficiency estimate may be more sophisticated, based on incorporatingconsideration of the estimated interferer channel quality, e.g., SINR.In such cases, the cancelation efficiency of the device 12 ischaracterized as a function of interfering-signal transport format andas a function of interfering-signal channel quality, so the determinedmapping can be indexed or otherwise used to find an accurate estimate ofcancelation efficiency in the current transmission interval with respectto a given interferer cell 18.

In at least one embodiment, a cancelation efficiency mapping table takeson the form of CE=F1(SINR, TF). Here, “CE” denotes cancelationefficiency, and “F1” connotes a function of interfering-signal transportformat and interfering-signal channel quality, e.g., SINR. The F1function or table thus is used to estimate the CE for each interferercell 18 of interest at the victim device 12 during the currenttransmission interval. The mapping table may be obtained from the device12 or constructed by the radio node 20, e.g., based on previousinterference-cancelation capability signaling from the device 12.

The radio node 20 then uses one or more of the following combinations ofinformation to estimate, i.e., “synthesize”, an accurate own-cellchannel quality estimate for the device 12 in the current transmissioninterval. That estimate is based on the estimated cancelationefficiencies of the device 12 with respect to the interferer cells 18,which efficiencies are more accurately known in view of the radio node20 knowing the actual transport format(s) to be used by the interferercell(s) 18 during the current transmission interval. The radio node 20then uses the own-cell channel quality estimate to perform linkadaptation towards the device 12 in the current transmission interval,e.g., to select the appropriate transport format to use for the own-celltransmission towards the device 12, and may also select precoding andrank settings for the own-cell transmission and, optionally, for one ormore of the interferer-cell transmissions.

Consider a more detailed example. A served device 12 has reported in aprior transmission interval its own-cell channel quality. In particular,the device 12 reported a set or range of own-cell channel quality valuescorresponding to a set or range of interfering-signal transport formats.Such a set or range of own-cell post-IC channel quality values may bereported for each interferer cell 18 of interest. That is, the device 12assumed or predicted the transport formats used by one or moreinterferer-cells 18 of interest in the prior transmission interval, andcorrespondingly calculated what its post-IC own-cell channel qualitywould be for each of those predictions or assumptions. Thus, the set orrange of own-cell channel quality values reported may comprise a matrixor table of values, e.g., with each row/column representing thetransport format assumption for a different one of the interferer cells18 of interest, and with each entry representing the resulting own-cellpost-IC channel quality value. Alternatively, indexing may be by assumedper-cell cancellation efficiency values, rather than assumed transportformat values.

Then, for a current transmission interval where it is assumed that thesame interferer cells 18 are of interest with respect to the device 12,the radio node 20 determines the expected cancelation efficiency of thedevice 12, where that determination is based on actual knowledge of thetransport formats that will be used by the interferer cells 18 ofinterest. For example, the own-cell post-IC channel quality estimatedfor the device 12 for the current transmission interval is computed bycombining the channel quality gains associated with the known transportformats for all of the interfere cells 18 of interest. Each of thosegains may be determined from the reported table or matrix of channelquality values, based on finding the entries that best match thetransport formats known for the interferer cells 18 for the currenttransmission interval and/or interpolating between the entries thatbracket the known transport formats.

Such processing can be seen as taking the assumed IC gains as reportedby the device 12 in the prior transmission interval and adapting them asneeded in view of the radio node having actual knowledge of thetransport formats that will be used by the interferer cells 18 in thecurrent transmission interval. The own-cell channel quality is thencomputed for device 12 for the current transmission interval bycombining the adapted channel quality gains, and the radio node 20 thenadvantageously schedules the maximum-size transport format that issupported by the thus-synthesized channel quality estimate.

Note that in cases where the device 12 is served by a pico cell 18-1that is interfered with by a macro cell 18-1, it may be that pico-celltransmissions generally do not interfere with macro-cell transmissions.In such instances, the radio node 20, alone or in combination withanother network node, may be configured to select the transport formatfor a macro cell transmission in the current interval first, thenestimate the resultant own-cell post-IC channel quality for the device12, and then use that own-cell channel quality estimate to select thebest transport format for serving device 12 from the pico cell 18-1 inthe current transmission interval.

In other embodiments, the scheduling process may include simultaneouslyscheduling several IC-capable devices 12 within a set of neighboringcells 18, transmissions to which are mutually interfering. In suchcases, the link adaptation teachings herein may be applied iteratively,to arrive at a robust transport format selection for all suchsimultaneously scheduled devices 12. This approach can be understood asjointly processing or otherwise optimizing the transport formatselection for such devices 12.

In a more detailed example embodiment, consider the heterogeneousnetwork environment illustrated in FIG. 1. FIG. 5 provides an examplesignal flow between a serving radio node 20 and a served device 12 inaccordance with this example. The below-detailed operations reflect anexpanded description of the illustrated signal flow.

At serving cell allocation time, the device 12, denoted as “UE” in FIG.5, signals that it is IC-capable via higher-layer signaling and signalsits cancelation efficiency, CE, performance. For example, the device 12sends a table CE=F1(SINR, TF). The table expresses the device's CE as afunction of interfering-signal channel quality and interfering-signaltransport format. In one embodiment, the transmitted mapping table mayconsist of CE values for a fixed or custom sampling of transport formatsand SINR values. CE values for transport formats and SINR values notrepresented in the table are found by the serving radio node 20, denotedas “NW” in FIG. 5, using, e.g., interpolation and/or extrapolation. Forexample, the device 12 transmits CE values for six predeterminedtransport formats and eight SINR values, where the SINR range may bepredetermined for each transport format assumed for reporting. Thisapproach results in fewer than fifty values per table. The serving radionode 20 can remap the reported CE values to CE values corresponding toactual transport formats known for any given current transmissioninterval.

At infrequent intervals, e.g. once per several seconds, the device 12determines the potentially interfering neighbor cell(s) 18, e.g. bymeasuring the received pilot/CRS power for neighbor cells 18. The device12 signals a list of dominant interfering Cell IDs to the serving radionode 20 via higher-layer signaling.

In the heterogeneous network scenario, typically only the macro cell18-2 will be reported as an interfering cell 18. At each TTI, the device12 transmits a channel quality report, e.g., a CSI report, with respectto the interfering macro cell 18-2. The channel quality report is validfor the transmission interval in which it is reported, and for asubsequent interval in which it is used by the radio node 20 to performlink adaptation towards the device 12 in that subsequent transmissioninterval. From the perspective of the device 12, it reports channelquality for the current transmission interval. From the perspective ofthe radio node 20, it performs link adaptations in a currenttransmission interval, using channel quality information reported by thedevice 12 in a prior transmission interval.

For the channel quality report sent by the device 12 in eachtransmission interval, the device 12 also transmits a table of own-cellchannel quality values as a function of macro-cell CE. For example, thedevice 12 sends CSI_sc=F2(CE_ic1, CE_ic2, . . . ). Here, “F2” can beunderstood as providing a set or range of channel quality values, e.g.,CSI values, as a function of different cancelation efficiencies assumedor predicted by the device 12 for interference cancelation with respectto the macro cell 18. That is, CE_ic1, CE_ic2, etc., represent differentown-cell post-IC channel estimates for different cancelation efficiencyassumptions with respect to an interferer cell 18 of interest. Assumingthat the macro cell 18-2 is the only interferer cell 18 of interest, thedevice 12 computes the own-cell channel quality it would see afterinterference cancelation with respect to the macro cell 18-2, for eachone in a set or range of assumed macro-cell signal transport formats.

When such processing is performed for only one interferer cell 18 ofinterest, the own-cell CSI table, the F2 table, is only one-dimensional.However, the approach extends directly to the case where multipleinterferer cells 18 are considered, by reporting a set or range ofown-cell channel quality values for a given set or range of assumedcancelation efficiencies for each interferer cell 18 of interest. Foreach interferer cell 18 of interest, the reporting may be limited to amanageable set or range of CE assumptions, e.g., CE=0, 0.25, 0.5, 0.75,and 1. A CE value of zero means no cancelation and a CE value of 1 meansfull cancelation.

For semi-static or slowly changing environments, the own-cellCSI-versus-interfering-signal transport format table may be valid overmany transmission intervals. In some embodiments, therefore, the tableis updated in its entirety at regular intervals. The update intervaldepends on the temporal variability of the channel, e.g., Doppler. Inother embodiments, the table may be updated by the device 12incrementally over several transmission intervals, at a relatively lowsignaling rate.

At any case, in the example scenario where the serving radio node 20 isa low-power node handling the pico cell 18-1, the radio node 20 uses thechannel quality report received from the device 12 in an earliertransmission interval. In particular, the radio node 20 uses the tableand the transport format that is known to be selected for use in themacro cell 18-2 in the current transmission interval, to obtain anaccurate estimate of the own-cell channel quality that the device 12will experience in the current transmission interval, after interferencecancelation with respect to, “WRT” in FIG. 5, the macro cell 18.

To compute the own-cell channel quality estimate, the radio node 20 inone or more embodiments is configured to: obtain the macro cellscheduling decision for the current transmission interval; use thechannel quality report previously sent by the device 12 to estimate thecurrent channel quality of the interference link from the macro cell18-2 to the device 12; estimate the CE that will be achieved by thedevice 12 in the current transmission interval with respect to the macrocell 18-2, based on previously signaled F1 table; estimate the own-cellpost-IC channel quality for the device 12, for the current processinginterval, using the F2 table; and schedule the device 12 for the currenttransmission interval using the estimated own-cell post-IC channelquality.

The approach of signaling the table CSI_sc=F2(CE_ic1, CE_ic2, . . . )and basing the synthesis of the own-cell post-IC channel quality at thedevice 12 for the current transmission interval on the combination ofthe tables F1 and F2 provides the best performance with limitedsignaling capacity. For example, signaling is minimized byparameterizing the F2 table according to different CE levels, fordifferent interfering signal transport format assumptions, where theparameterized range provides good resolution for estimating the own-cellpost-IC channel quality at the device 12 for the current transmissioninterval, in view of actual knowledge of the transport format(s) thatare known to be selected for the interferer cell transmissions ofinterest in the current transmission interval.

FIG. 6 illustrates an example signal flow between a serving radio node20, denoted as “NW” in FIG. 6, and a served device 12, denoted as “UE”in FIG. 6, in an alternative approach. According the depictedalternative, the device 12 initially indicates itsinterference-cancelation capability, but sends conventional, legacychannel quality reports during normal operation. The below-detailedoperations represent an expanded explanation of the illustrated signalflow.

The device 12 signals its interference-cancelation capabilityinformation, e.g., at initial connection. The information may be sentdirectly to the radio node 20, or may be sent indirectly to the radionode 20 from another node in the network 10. The device 12 signals ateach transmission interval a CSI table that is parameterized byinterfering cell transport format. For example, the F2 table can beformed as CSI_sc=F2(TF_ic1, TF_ic2, . . . ). Here, TF_ic1, TF_ic2, etc.,represent different own-cell channel quality values for differentinterfering-signal transport format assumptions. In this approach, theinitial signaling of table F1 is not necessary. Preferably, the table F2contains entries for a sparse set of transport formats and the radionode 20 is configured to interpolate the CSI values for transportformats not included in the F2 table.

Another example of the teachings herein may be formulated where thedevice 12 only uses legacy channel quality reporting. A typical scenariois where the device 12 has low intensity traffic and the network 10wishes to minimize the uplink, UL, control signaling. Another scenariofor this example is when the device 12 cannot, due to complexity,perform the previously described signaling.

Accordingly, when the device 12 connects to a serving radio node 20, ittransmits its IC capability to the radio node 20. During activemode—i.e., during ongoing connected operation—the device 12 transmits atregular or irregular intervals, legacy channel quality reports withrespect to the own-cell. These legacy channel quality reports are basedon the kind of reporting that would be done by a linear, non-ICreceiver.

In turn, in such embodiments, the radio node 20 uses the own-cellchannel quality reported received from the device 12 in a previoustransmission interval to estimate the own-cell post-IC channel qualityexpected for the device 12, for the current transmission interval. Withthat estimate, the radio node 20 schedules an optimal transport formatfor the current transmission interval. The synthesis is performed by:(1) estimating the interfering cell channel quality based on thereported own-cell channel quality, the known previous subframeinterfering transport format and the determined CE mapping table for thedevice 12; (2) and estimating the own-cell post-IC channel quality thatwill be experienced at the device 12 in the current subframe, based onthe known interfering-signal transport format and the determined CEmapping table.

As an example of the processing contemplated in the foregoing Item (1),consider the case where the radio node 20 has a mapping table that mapsthe CE of the device 12 as a function of interfering-signal channelquality and interfering signal TF. The reported own-cell channel qualityin this case is a post-IC value, thus reflecting the CE achieved by thedevice 12 with respect to the interfering signal. The radio node 20therefore infers the CE from the reported own-cell channel quality. Itthen uses the inferred CE in combination with the TF known to be usedfor the interfering transmission from the neighbor cell 18, to indexinto the mapping table and find or derive the correspondingneighbor-cell channel quality. Thus, the mapping table is used in areverse sense, to estimate the neighbor-cell channel qualities.

The mapping table can be a static table which is based on a typical ICreceiver performance for the device's reported IC capability class.Alternatively, the mapping table is updated and adapted over an extendedtime, using the observed performance of many devices 12 for each ICreceiver capability class. The updating mechanism is based in one ormore embodiments on reported ACK/NACK from the devices 12 whoseperformance is observed, and knowledge of the interfering-signaltransport formats at issue with respect to those ACK/NACKs. Reportedinterferer cell channel quality and transmission rank also may beconsidered. Note, too, that some types of communication networks supportconventional channel quality reporting with respect multiple basestations. When the teachings herein are applied in such networks, themulti-cell channel quality reporting can be exploited using knowntransport format information for interfering signals transmitted in thecells for which channel quality was reported. That is, the separateinterfering-cell channel quality reports allow a radio node 20 that isconfigured according to the teachings herein to account more preciselyfor different interfering transport formats from different interferingcells 18 at the current transmission interval.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

What is claimed is:
 1. A method of channel quality reporting by awireless device configured for operation in a cellular communicationnetwork, said method comprising: sending interference-cancelationcapability information to the network, indicating one or morecharacteristics of interference-cancelation processing the device isconfigured to perform; generating a channel quality report for a servingradio node in the network with respect to a current transmissioninterval, based on: determining a neighbor-cell channel quality withrespect to a neighbor cell originating a neighbor-cell transmissionusing a selected transport format, wherein the neighbor-celltransmission was detected by the device as an interfering transmissionin the current transmission interval; determining, with respect to theserving radio node, a set or range of own-cell channel quality valuesversus different interference cancelation efficiencies assumed for theinterfering transmission, or versus different transport formats assumedfor the interfering transmission, wherein the interference cancelationefficiency of the device with respect to the interfering transmissiondepends on which transport format was used by the neighbor cell for theinterfering transmission; and transmitting the channel quality report tothe serving radio node.
 2. The method of claim 1, further comprisingidentifying the neighbor cell for inclusion in the channel qualityreport based on: sending an indication to the serving radio node thatthe neighbor cell is an interfering neighbor cell; and receiving areturn indication identifying the neighbor cell as being an interferercell of interest to include in channel quality reporting.
 3. The methodof claim 2, further comprising sending updated indications to thenetwork from time to time, as to which neighboring cells are seen asinterfering cells by the device, and receiving corresponding updatedreturn indications as to which neighbor cell or cells are interferercells of interest to include in the channel quality reporting.
 4. Themethod of claim 1, wherein sending the interference-cancelationcapability information comprises sending an indication as to whether thedevice is configured to perform pre-decoding interference cancelation orpost-decoding interference cancelation.
 5. The method of claim 1,wherein sending the interference-cancelation capability informationincludes sending mapping information that maps a set or range ofinterfering-signal transport formats to a corresponding set or range ofinterference cancelation efficiencies of the device.
 6. A wirelessdevice configured for operation in a cellular communication network,said device comprising: a signaling interface configured to send signalsto the network and receive signals from the network; a processingcircuit operatively associated with the signaling interface andconfigured to: send interference-cancelation capability information tothe network, indicating one or more characteristics ofinterference-cancelation processing the device is configured to perform;generate a channel quality report for a serving radio node in thenetwork with respect to a current transmission interval, based on beingconfigured to: determine a neighbor-cell channel quality with respect toa neighbor cell originating a neighbor-cell transmission using aselected transport format, wherein the neighbor-cell transmission wasdetected by the device as an interfering transmission in the currenttransmission interval; determine a set or range of serving-cell channelquality values versus different interference cancelation efficienciesassumed for the interfering transmission, or versus different transportformats assumed for the interfering transmission, wherein theinterference cancelation efficiency of the device with respect to theinterfering transmission depends on which transport format was used bythe neighbor cell for the interfering transmission; and transmit thechannel quality report to the serving radio node via the signalinginterface.